there is nothing qierd about it.
an ATX psu can supply the power for it.
You should repair its own amplifier, it will be more than sufficient for a livingroom given 4 ohm rated speakers as load.
You may wish to hack the pc psu to obtain 13.2 volts insted of the stock 12 volt , but it should not be needed.

i dont think i want to use atx psu and the low voltage amplifier that puts out max of 10W PMPO...
It has terrible amplifier, i have 8R floorstanders that want at least 2W of pure power to make some hearable sound.
I will probably use +-28V from dual 20V, single ~10V 250VA toroid transformer.
I can get higher voltage anytime whenever i rewind the transformer.
I will probably build 12" subwoofer enclosure and plateamp too by myself maybe with some 89 series of TDA class D chipamps maybe 8950 who knows..

ATX psu puts out too much heat, even when idle and its waste of time adding better cooling, i hate fans.

Passive monster cooling all the way.

I only wanted the FM block, its super well shielded and i just love the stereo sound of it, but need to hook it up to TV and PC to watch movies and such.
I also play many games, maybe I'll need surround decoder and 5 channels...

It might turn into lack of problems and become expensive, who knows...